fix: protect qdocco source files

[tiye]

Summary

• reject qdocco output paths that resolve to the input source
• protect against accidental overwrite through symlinks as well as identical paths
• add a CLI regression test and document the RFC 0083 safety contract

Validation

• make check
• focused qdocco regression test
• git diff --check

This PR is chained after PR #40 and is intentionally not merged automatically.

[Copilot]

Pull request overview

This PR hardens the qdocco CLI against accidentally overwriting its input source by rejecting output paths that resolve to the same file (including via symlinks), and codifies the safety contract in both tests and RFC documentation.

Changes:

• Add a same_path() guard in qdocco to reject output paths that match the input source after canonicalization (exit code 2).
• Add a CLI regression test covering the “output equals input” overwrite scenario.
• Document the safety contract in RFC 0083.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/cli_tools.rs	Adds a regression test to ensure qdocco -o cannot overwrite the input source file.
src/bin/qdocco.rs	Introduces a canonicalized path equality check to prevent input source overwrites.
RFCs/0083-qdocco-markdown.md	Documents the “output must differ from input (incl. symlink)” contract as part of the CLI spec.

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